Vacuum deposited light-sensitive titanium dioxide



United States Patent 3,547,635 VACUUM DEPOSITED LIGHT-SENSITIVE TITANIUM DIOXIDE Kenneth C. Kennard and John A. Haefner, Rochester,

N .Y., asssignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed May 4, 1967, Ser. No. 636,016 Int. Cl. G03c 5/24 US. Cl. 96-48 7 Claims ABSTRACT OF THE DISCLOSURE Photographic elements comprising a support coated with a thin layer of vacuum deposited titanium dioxide can be developed to produce photographic images. Such elements can be reused, and are amenable to deletions from and additions to existing image areas.

This invention relates to photography, and particular- 1y, to reusable, non-silver halide photographic elements and the preparation of images therewith.

Presently known photographic elements are typically characterized by the dispersing of photographic material (silver halide, for example) in a hydrophilic binder such as gelatin. The processing of such photographic elements is complicated by the necessity of permeating the binder in order to treat the photosensitive material with a processing solution. Moreover, after development, an extended drying period is demanded to optibize the resistance of the element to abrasion and other deterioration. It is also a drawback of hydrophilic binder materials that they tend to absorb moisture, which when present can significantly lessen the storage life of the photographic elements, as well as deleteriously affecting its other photosensitive properties. Additionally, typical photographic elements incorporating hydrophilic binder materials are susceptible of being utilized only once. Other disadvantages of binder-containing photographic elements are the limitations of fine detail recording imposed by particle size and the difficulties of applying a hydrophilic binder material to hydrophobic supports.

Also known in the art are photographic elements incorporating, as the photosensitive material, photoconductive materials such as zinc oxide and titanium dioxide. Elements of this type are susceptible of light storage prior to exposure and development, requiring only a short period of dark adaptation during which time heightened photosensitivity is obtained. Moreover, although these elements can be re-exposed, permitting the formation of any successive number of latent images, processing produces a permanent visible image which, although it can be supplemented, cannot be removed. Additionally, they also incorporate a binder material and, as such, are subject to the previously described disadvanatges associated therewith.

It is known to produce binderless, photographic elements by vacuum depositing a thin, microcrystalline layer of silver halide upon a support material, thus avoiding the problems associated with the presence of a binder material. Such binderless photographic elements are, however, light sensitive and must be continuously stored in dark conditions prior to exposure and development. Moreover, such binderless photographic elements are susceptible of but one use, and once an image has been permanently recorded, no additions or deletions can be made.

Accordingly, it is an object of the invention to provide a novel binderless photographic element.

It is also an object of the invention to provide a new photographic element which can be stored under lighted conditions prior to exposure and development.

An additional object of the present invention is to provide a novel photographic element which can be reused.

Yet an additional object of this invention is to provide a new photographic element which is, after development, suceptible of addition to and deletion from the developed image.

Still another object of the instant invention is to provide a novel photographic process for the production of photographic images.

Yet additional objects of the present invention will become obvious from a consideration of the following specification and appended claims.

The objects of this invention are accomplished with reusable photographic elements comprising a support having coated thereon a binder-free light-sensitive layer comprising titanium dioxide. The light-sensitive titanium dioxide layers which are employed in the practice of the invention described herein are thin, abrasion resistant layers of titanium dioxide deposited, without a binder, upon a support material by vacuum deposition techniques.

The choice of a suitable support upon which to coat the photosensitive titanium dioxide is subject to Wide variations, and is limited only by the use to which the completed photographic element will be applied and those temperatures incurred during the actual vacuum deposition. Glass is suitably employed as are metals such as aluminum, copper, zinc and tin. Conventional photographic film bases, such as cellulose acetate, cellulose acetate bytyrate, poly(ethylene terrephthalate), polystyrene, polyethylene-coated paper and paper are all susceptible of advantageous use.

The coating operation is accomplished by well-known vacsuum deposition techniques, such as those described for vacuum depositing silver halide as in US. Pat. No. 1,970,496. Typically, the support material is placed within a scalable enclosure along with titanium dioxide. Alternatively, metallic titanium can be used as the source of titanium dioxide by introducing oxygen into the vacuum system. The enclosure is sealed, the pressure reduced and the temperature elevated, which combination of conditions produces the sublimation of titanium dioxide microcrystals upon such support material.

Coating thickness can be typically varied between about 40 angstroms and 2.5 microns, with thicknesses of between .05 micron and 1.5 microns preferred. At substantially less than 40 angstroms, there is insufficient titanium dioxide present to afford adequate photographic sensitivity, and when coatings are prepared at thicknesses significantly in excess of 3 microns, photographic response declines.

The coatings advantageously produced according to the methods described herein are substantially transparent since the crystalline particles deposited by vacuum techniques are extremely small. Accordingly, such coatings do not inhibit the versatility of an otherwise transparent support material where, for example, the subsequent projection of an image is intended. Additionally, no protective coatings are required since the vacuum deposited titanium dioxide is an abrasion and solvent resistant layer which tenaciously adheres to the surface of the support material.

A photographic element coated as described hereinabove can be stored under lighted conditions. If it is so stored, then immediately prior to exposure it must be dark adapted. Dark adaption constitutes storing the titanium dioxide coated support under dark conditions for a time sufficient to raise the resistivity of the titanium dioxide to a point where the ratio of dark resistivity to light resistivity is sutficiently great to permit the development of a suitable dense photographic image. The length of this period of dark conditioning depends in part upon the intensity with which the element has been previously exposed and the intensity with which it will receive its intended imagewise exposure. Typically, however, dark adaptation of from about to about 24 hours will insure adequate photographic response. Alternatively, storing the photographic element under conditions of elevated temperature may enhance photosensitivity.

The photographic elements described hereinabove are exposed imagewise through an original pattern, producing a latent charge image corresponding to the exposed and unexposed areas. The presence of such a charge distribution renders the photographic element amenable to development. The titanium dioxide layers on the present photographic elements are sensitive to ultraviolet light, and hence, exposing means rich in ultraviolet light are preferred. However, sensitizing dyes can be used to make the titanium dioxide sensitive to the visible portions of the spectrum.

Development of a latent image in the present photographic elements is preferably a two-step physical development sequence. Initially, the imagewise exposed element is treated with a solution typically containing silver ions. Such a solution can be, for example, an aqueous solution of a silver salt such as silver nitrate, silver chloride, silver sulfate, etc., and treatment therewith produces microscopic deposits or development centers of metallic silver in the exposed areas. The treating technique can be by immersion, swabbing, spraying and any other means whereby sufiicient solution contacts the exposed element.

Subsequent to the treatment with a solution preferably containing silver ions, the imagewise exposed photography element is treated with a physical developer solution containing heavy metal ions and a reducing agent for the metal ions, and when the metal ion salt is substantially insoluble in water, a solvent for the metal ion salt, such as water-soluble thiosulfates, thiocyanates etc. to produce a visible photographic image corresponding to the exposed areas. Typical physical developer solutions are well known (see Hornsby, Basic Photographic Chemistry (1956), 66, and Mees and James, ed. The Theory of the Photographic Process, 3rd ed. (1966), 329-331) and contain the metallic ions such as silver, copper, iron, nickel and cobalt necessary to form a visible image at and in the vicinity of nucleating centers, the microscopic metal deposits created during the above-described first step. Typical reducing agents used in the physical developer include, for example, polyhydroxy-substituted aryl compounds such as hydroquinones, catechols and pyrogallols; ascorbic acid derivatives; aminophenols; p-phenylenediamines, and the like, developing agents used in the photographic art. Particular examples of reducing agents for physical developer solutions are 2-methyl-3-chlorohydroquinone, bromohydroquinone, catechol, S-phenylcatechol, pyrogallol monomethyl ether (1 methoxy 2,3 dihydroxybenzene) and S-methylpyrogallol monomethyl ether, isoascorbic acid, N-methyl-p-aminophenol, dimethyl-p-phenylene diamine, 4 amino N,N di(n-propyl)aniline and 6-amino-1-ethyl- 1,2,3,4-tetrahydroquinoline. The completely developed element carries a visible image, typically metallic silver, corresponding to the exposed areas. As such, it is a negative reproduction of the original pattern, and when a negative serves as the original pattern, positive copies are obtained.

The above-described photographic elements, as developed, can be employed where images must be projected. The vacuum deposited titanium dioxide layers are themselves preferably transparent, and when coated upon a transparent support, they can provide developed elements which comprise an opaque image upon a support which is still transparent in the non-image areas.

Additionally, such photographic elements as are described herein are susceptible of advantageous reuse.

The visible metallic image formed upon development does not penetrate beneath the surface of the titanium dioxide layer and can be removed by treatment with organic solvents, acids, bases or even by reasonable scrubbing with abrasive scouring powder. Such treatment does not deleteriously affect the light-sensitive, vacuum deposited titanium dioxide layer since it possesses an extremely hard surface and adheres tightly to the surface of the support. Once the image is removed, the photographic element need only be dark adapted as described hereinabove to increase its photosensitivity and it can then be re-exposed and redeveloped. Such a removal of visible surface image cannot be readily effected if the titanium dioxide is coated as a dispersion in a hydrophilic colloidal material.

Along similar lines, only a portion of an image need be removed, since treatment with a solvent or an abrasive can be restricted to only part of the image area. In such fashion, these images are susceptible of selective deletion.

The photographic elements described herein also exhibit an add-on potential, and developed elements can be reused to add additional image area. After one or a series of developments, the non-image areas remain photosensitive and require only a period of dark adaptation to increase this sensitivity, after which time the photographic element can be re-exposed and redeveloped to form additional image. Such adding-on can be effected any number of times, with the only limitation being the availability of non-image area.

These photographic elements also exhibit utility in image-transfer operations. As noted above, the image does not penetrate the surface of the titanium dioxide layer. Hence, the image can be partially removed merely by contact with an image receiver having a more adherent surface. If the image receiver comprises a transparent support, right-reading copies can be produced merely by contacting the image with the adhesive layer and then separating the two. In such fashion, a plurality of copies can be produced.

The utility of such photographic elements and processes as are described above will become increasingly obvious from the following examples, which serve only to illustrate particular embodiments of the present invention, and are not intended as limitations thereof.

EXAMPLE 1 A flat glass support to which has been applied a nm thick layer of titanium dioxide by vacuum deposition means at a temperature of about C. and a pressure of about l0 torr is dark adapted for 18 hours. The titanium dioxide coated glass plate is then exposed through a negative to a No. 2 photoflood tungsten light source for a period of 30 seconds and at a distance of about 12 inches from the exposing plane. The exposed plate is then immersed in a 1% ethanolic silver nitrate solution for 20 seconds, after which it is sequentially washed with distilled water and immersed for two minutes in a physical developer solution having the formula PART A Water: 800 cc.

Sodium sulfite: 20 g.

Sodium isoascorbate: 26 g.

Sodium carbonate (monohydrate): 50 g.

Octylphenoxyethoxy ethyldimethyl p chlorobenzyl ammonium chloride (1% in H 0): 22 cc.

Water (pH-1LO) to 1 liter PART B Water: 800cc.

Sodium thiosulfate .SH O: 30 g.

Silver chloride: 5X10 moles Water to 960 cc.

S-methylbenzatriazole (1% in dil. KOH): 40 cc.

wherein Parts A and B are mixed just prior to use. For making the silver chloride used in Part B, 42.4 g. of silver nitrate are dissolved in 900 cc. of water, and 42.4 g. of potassium chloride is dissolved in a second 900 cc. of water. Then, 90 cc. of each solution are mixed in 6 ounce bottles which are allowed to stand overnight, after which time the liquid is poured off. The contents of two such bottles is required to make the 10 moles, since each contains 2.5 X moles of silver chloride. After development, a dense silver image is present in the exposed areas.

EXAMPLE II A photographic element like that used in Example I is dark adapted, exposed and developed as in Example 1, producing a dense silver image in the exposed areas. The image is then removed by treatment with chromic acid. After a second dark adaptation, exposure and development as in Example I, a dense silver image forms in the exposed areas of the second exposure.

EXAMPLE III According to the procedure described in Example I, a 1.2 layer of titanium dioxide is vacuum deposited upon a poly(ethylene terephthalate) support material. The coated support is then exposed to a source rich in ultraviolet light through a standard .15 Log E neutral density increment step wedge and developed as in Example I. A silver image of varying density is produced in the exposed areas, such densities corresponding to the density increments on the step wedge.

EXAMPLE IV A photographic element like that described in Example III is exposed and processed as in Example I, except that half of the sample is covered during exposure. The developed sample is dried in the dark (omitting the necessity for a second period of dark adaptation), and the unexposed half is exposed and processed as before, producing a silver image in the previously undeveloped half. With sequential dark adaptation, exposure and development, additional images can be produced over and over.

EXAMPLE V A photographic element as described in Example I is dark adapted, exposed and processed in like manner. A dense silver image is produced in the exposed areas. This image is brought into contact with a transparent polymeric sheet whose contacting face is coated with a tacky material. Upon separating the two, a copy of the image is observed on the adhesive coated receiving sheet, which image is an identical copy when viewed through the receiving sheet.

The invention has been described in considerable detail with reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A reusable photographic element comprising a support having coated thereon a thin, binder-free, vacuum deposited light-sensitive layer comprising titanium dioxide, said layer having a thickness of from about 40 angstroms to about 2.5 microns.

2. A reusable photographic element as described in claim 1, wherein the support comprises poly(ethylene- 60 terephthalate) 3. A reusable photographic element as described in claim 1, wherein the support comprises glass.

4. In a process for physically developing an imagewise exposed photographic element to produce a photographic image, the improvement which comprises utilizing a reusable photographic element comprising a support having coated thereon a thin, binder-free, vacuum deposited light-sensitive layer comprising titanium dioxide, said layer having a thickness of from about 40 angstroms to about 2.5 microns.

5. A process for treating an imagewise exposed photographic element, 'Which comprises a support having coated thereon a thin, binder-free, vacuum deposited lightsensitive layer of titanium dioxide, said layer having a thickness of from about 40 angstroms to about 2.5 microns, to produce a photographic image, said process comprising sequentially (1) treating said photographic element with a first solution comprising a silver ion-containing solution to produce development centers of metallic silver in the exposed areas, and thereafter (2) treating said photographic element with a physical developer solution containing silver ions and a re ducing agent for a time sufficient to produce a visible metallic silver image in the exposed areas.

6. A photographic process as described in claim 5 wherein the said first solution comprises silver nitrate.

7. A photographic process as described in claim 5 wherein the said physical developer solution has a formula consisting of equal portions of Parts A and B, wherein:

Part 13 consists of:

Water: 800 cc.

Sodium thiosulfate .5H O: 30 g.

Silver chloride: 5 X 10- moles Water to 960 cc.

S-methylbenzatriazole (1% in dilute potassium hydroxide): 40 cc.

References Cited UNITED STATES PATENTS 9/1959 Reichelt 117-34 1/1969 Berman et a1 96-48 NORMAN G. TORCHIN, Primary Examiner J. L. GOOD-ROW, Assistant Examiner US. Cl. X.R. 

